The need to separate emulsions of water and hydrocarbons is ubiquitous; historically impacting a broad array of industries. The separation of water-hydrocarbon emulsions has conventionally involved systems that rely on single or multiple elements, novel flow patterns, stilling chambers, parallel metallic plates, oriented yarns, gas intrusion mechanisms, and electrostatic charge. The balance of separation systems employ an element that contains a fibrous, porous coalescing media through which the emulsion is passed and separated. Irrespective of the system design, all water-hydrocarbon separation systems target the collection of emulsified drops into close proximity to facilitate coalescence. Coalescence and subsequent separation due to density differences between water and hydrocarbons is the mechanism behind all separation systems.
Conventionally known fibrous, porous coalescence media induce emulsion separation in flow-through applications through the same general mechanism, irrespective of the nature of the emulsion. The coalescence media presents to the discontinuous phase of the emulsion an energetically dissimilar surface from the continuous phase. As such, the media surface serves to compete with the continuous phase of the emulsion for the discontinuous, or droplet, phase of the emulsion. As the emulsion comes in contact with and progresses through the coalescing media, droplets partition between the solid surface and the continuous phase. Droplets adsorbed onto the solid media surface travel along fiber surfaces, and in some cases, wet the fiber surface. As more emulsion flows through the media, the adsorbed discontinuous phase encounters other media-associated droplets and the two coalesce. The drop migration-coalescence process continues as the emulsion moves through the media.
A coalescence media is therefore typically considered to be functionally successful for breaking a given emulsion if the discontinuous phase preferentially adsorbs or is repelled and if the droplet phase has been coalesced into drops at the point of exit from the media that are sufficiently large to allow their separation from the continuous phase. Typically, the drops separate from the continuous phase as a function of density differences between the liquids involved. Conversely, a coalescence media is considered to be functionally unsuccessful for breaking an emulsion if the drops remain sufficiently small at the point of exit from the media that they remain entrained by the continuous phase and fail to separate.
Conventional fibrous, porous coalescence media are known which effectively remove over 90 wt. % of emulsified water from a hydrocarbon, when the hydrocarbon has an interfacial tension (γ) above 25 dynes/cm with water. If the hydrocarbon displays hydrocarbon-water interfacial tension below 25 dynes/cm (colloquially known as “sub-25 interfacial tension hydrocarbons”), the water-hydrocarbon emulsion is considerably more tenacious and the ability of prior art emulsion separation media to remove emulsified water diminishes dramatically to the point where 40-100 wt. % of emulsified water is allowed to pass into the end use without removal.
A decrease in hydrocarbon interfacial tension occurs when the hydrocarbon is dosed with surfactants. In this regard, one root cause of prior art fibrous, porous coalescence media failure in sub-25 interfacial tension hydrocarbons is the presence of increased surfactancy. In cases of sub-25 interfacial tension hydrocarbons, emulsion separation requires more complex systems that often involve nested pleated elements, flow path controllers, wraps, and stilling chambers. The prior art is replete with examples of complex systems designed to manage difficult to separate water-hydrocarbon emulsions. Therefore the need for a universal media capable of emulsion separation irrespective of hydrocarbon-water interfacial tension or surfactant content is clear in the face of such complexity.
The role of surfactant-deactivation of conventional fibrous, porous coalescence media includes drop size, drop stability, and surfaces. Surfactants are molecules that contain both hydrophilic and hydrophobic moieties. When present in a hydrocarbon-water mixture, surfactants align at interfaces with the hydrophilic head group associated with the water-like phase, and the hydrophobic tail extended into the oil-like phase. This is the lowest energy conformation of the surfactant, and it results in depressed hydrocarbon-water interfacial tension. As a result of depressed interfacial tension, a given increment of input energy to the hydrocarbon-water mixture will result in a higher interface surface area in the presence of a surfactant. Interface surface area is inversely proportional to discontinuous phase drop size. Thus, in the presence of surfactant, a given increment of input energy will result in a smaller drop size distribution of discontinuous phase than in the absence of surfactant. In this regard, all fuel-water separation media rely on physical interaction between water drops and the media to effect separation. Surfactants create sufficiently small water drops that many pass through the media without encountering it. Surfactants also stabilize the emulsion from separation so that drops that do impact the media are less likely to partition out of the fuel onto the media. Similarly, drops that impact other drops resist coalescing into the larger drops necessary for successful separation. Finally, surfactants associate with surfaces of media and water drops, and interfere with the unique surface interactions between media and water that destabilize water within the fuel and allow its separation. Collectively, the result of blending surfactants into a hydrocarbon is deactivation of the prior art fibrous, porous coalescence media and escape of water into the end use.
The need for a fibrous, porous coalescence media that removes water independent of hydrocarbon interfacial tension has become substantially more pronounced with mandated changes in diesel fuel quality. In the 2007 Heavy Duty Highway Diesel Rule, the EPA mandated respective reductions of particulate (PM2.5) and nitrogen oxide (NOx) emissions of 90% and 92%, with NOx allowances to drop an additional 3% in 2010. At the time of the mandate release, sulfur sensitive exhaust after-treatment was considered necessary to meet 2007 emission goals. As a result, the 2007 Highway Rule also requires sulfur levels in diesel fuel to drop 97% to 15 ppm. The resulting ultra low sulfur diesel fuel (ULSD) has been stripped of its native lubricity and requires surfactant addition to meet engine wear control requirements. ULSD consistently manifests sub-25 interfacial tension hydrocarbons with water. EPA mandated diesel fuel requirements will cascade into off-road diesel, rail, and marine fuels as part of the EPA's tiered approach to emission control, indicating all non-gasoline transportation and power generation fuels will converge over time at sub-25 dynes/cm interfacial tension.
In addition, various governmental regulatory agencies in the United States have begun providing incentives for or simply mandating minimum biodiesel blend components for commercial transportation fuels. Biodiesel is a blend of fatty acid methyl esters derived from caustic catalyzed methanol esterification of plant and animal triglycerides. Biodiesel is a surfactant, and fuel blends containing as little as 2% biodiesel have interfacial tensions well below 25 dynes/cm. As a result, the fuel pool available for non-gasoline transportation and power generation is rapidly transitioning to an interfacial tension region where prior art fuel-water emulsion separation media fail to remove water from the hydrocarbon.
Despite shifts in fuel interfacial tension, water remains a fuel contaminant of concern for corrosion of steel engine components and promotion of microbiological growth. All non-gasoline engines have fuel-water separation capability mounted in the fuel system. Further, engine emission compliance with the EPA 2007 Highway Rule depends heavily upon high pressure fuel injection equipment that is extremely sensitive to water. This makes fuel dewatering of higher importance for systems designed to meet the 2007 EPA emission mandates that spawned systemic change in fuel quality. Fuel mileage and operator interface requirements for engines dictate the need for small, light, and easy to operate water separation systems. These needs often preclude the complex separation systems that are conventionally known. As a result, mandated changes in fuel quality have created a well defined need for a fibrous, porous coalescence media that removes water independent of hydrocarbon interfacial tension.
Examples of novel coalescence media are described in commonly-owned, co-pending U.S. patent application Ser. No. 12/014,864 filed on Jan. 16, 2008 and entitled “Coalescence Media for Separation of Water-Hydrocarbon Emulsions” (the entire content of which is expressly incorporated hereinto by reference and will be referenced below as “the US '864 application”). These media achieve high surface area with needed pore structure and permeability and effectively separate tenacious emulsions of water and surfactant-containing hydrocarbons such as biodiesel-ULSD blends without use of complex separation systems. Media of the prior art often require multiple layers to affect the single function of separation of water-hydrocarbon emulsions, without guarantee of successful separation in high surfactant content, low interfacial tension hydrocarbons. In contrast, the media described in U.S. patent application Ser. No. 12/014,864 is formed as single dry layer from a wet-laid process using a homogenously distributed, wet-laid furnish including cellulose or cellulosic fibers, synthetic fibers, high-surface-area fibrillated fibers, glass microfiber, and a surface-area-enhancing synthetic material, which successfully performs the single function of water separation with a single layer of filtration media in low interfacial tension hydrocarbons.
It is typical for any fibrous, porous coalescence media to be part of a multi-layered media structure where some of the layers perform functions other than emulsion separation. In such cases, the layers may or may not be laminated together. Reasons to employ multiple layers can be due to media integrity concerns and/or filtration needs. Relative to media integrity, multiple layers are used to support the fibrous, porous coalescence media or the composite structure, to protect the fibrous, porous coalescence media from high speed rotary pleaters, and to protect the end use from possible migration of fibers from other media layers. Relative to filtration needs, multiple layers are used to add filtration capabilities such as particle removal, dirt holding, or impurity adsorption to coalescing performance. Impurities may consist of asphaltenes, organic moieties, salts, ions, or metals. In order to meet filtration goals as well as to protect media integrity, a layer on the downstream side of the coalescing media in a multi-functional filtration media is required.
Incorporation of a coalescing media into a multi-layered, multi-functional coalescing media structure with a layer on the downstream side of the coalescing layer creates the possibility of media failure in high surfactant (i.e., sub-25 interfacial tension) hydrocarbons due to re-emulsification of the previously coalesced drops. In this regard, coalesced water drops must be large enough to settle out of the hydrocarbon flow by virtue of density differences otherwise they will be carried out of the separating device with the dried hydrocarbon and re-emulsified therein. Coalescing media must therefore function to enlarge micron sized droplets of water found in high surfactant content water-hydrocarbon emulsions into millimeter sized coalesced water drops which can gravimetrically settle out of the dry hydrocarbon flow.
For the reasons noted above, in high surfactant content hydrocarbons, the performance of any coalescing layer in a multi-layered media can be dramatically reduced by media that is conventionally used on the downstream side of the coalescing layer. Specifically, conventional media situated on the downstream side of a coalescing layer include phenolic resin saturated cellulose wet laid media, polyester meltblown, spunbond, and meltblown-spunbond composites, and nylon spunbond. Such conventional media can and does dramatically reduce the coalescing function of the coalescence media in high surfactant-containing hydrocarbons. By way of example, the performance reduction that can be manifested through use of such conventional media downstream of a coalescing layer can be between about 50 to 100% of emulsified water remaining in the hydrocarbon and thereby being passed on to the hydrocarbon's end use due to reduction in droplet size of the previously coalesced water droplets.
It would therefore be desirable if new media options to serve as layers placed on the downstream side of a coalescing media could be provided that perform requisite support and protection functions as well as display sufficiently high surface area for water adsorption to minimize re-emulsification. In this regard, it would be especially desirable if a media serving as a layer downstream of a coalescing layer perform not only its traditional support and protection roles, but also provide for a higher surface area for water adsorption than the coalescing layer. Such a downstream layer would serve to expand the flow path available to water, and accordingly would induce the Venturi effect and reduce the water velocity relative to the hydrocarbon. Such a velocity reduction would in turn increase the water pressure within the downstream layer, thus forcing hydrocarbon out of the layer. These factors would serve to further separate water from hydrocarbon and thus facilitate further coalescence of the water. This is highly desirable for separation applications involving surfactant-containing hydrocarbons. It is therefore additionally desirable to develop media capable of providing support and protection functions demanded of media placed on the downstream side of a coalescing layer in a multi-layer coalescing media that provide higher surface area for water adsorption than available within the coalescing layer.
It is towards fulfilling such desirable attributes that the present invention is directed.